Estimation of dynamic characteristics of ground and structures with microtremor measurements- A supportive tool for strong ground motion instrumentation

Degree of damage during earthquakes strongly depends on dynamic characteristics of buildings as well as amplification of seismic waves. Determining these characteristics in advance and increasing durability of ground and structures beyond the presumed seismic force become a fundamental of earthquake disaster prevention.One way of investigating dynamic characteristics is to install strong motion seismometers and monitor structure continuously. For the effectiveness of this installation, vibration mode characteristic of the structures be clearly understand in advance. In this paper, usage of microtremor method as a supportive tool for strong ground motion instrumentation is presented. Since there is a growing interest to protect historical monuments, application of this method was made to the microtremor measurements performed at Suleymaniye Mosque located in Istanbul. In a short period of time present method provided several information including natural frequency, amplification factor and vibration mode characteristics of the mosque as well as its ground. Data showed that movement in longitudinal(NS) direction is larger than transversal(EW) direction. Vulnerability index, K values (Nakamura, 1997) is also calculated and several weak points of the mosque could be investigated. This approach help to understand the behaviors of old monuments as well as new buildings and can serve for retrofitting purposes.